Lutzomyia longipalpis, a sibling complex, is the main vector of Leishmania chagasi/infantum. Discriminating between siblings is important as they may differ in vectorial capacity. Lutzomyia ...longipalpis populations display distinct male sex pheromone chemotypes. We investigated the phylogeographic pattern of variation at microsatellite loci from 11 populations from Brazil and Venezuela related to their male pheromone. Temporal genetic differentiation was mostly not significant at the same site. Spatial genetic differentiation was, however, strong, although there was only a weak relationship between genetic differentiation and the geographic distance separating the samples (r2 < 0.10); geographic separation explained a much greater (54-97%) percentage of the genetic differences among populations when samples with the same pheromone type were analyzed separately. A cluster analysis showed five groups: Lu. cruzi (Brazil) and Lu. pseudolongipalpis (Venezuela) as separate species, two (mostly 9-methyl-germacrene-B) Venezuelan and Brazilian groups, and a very distinct cluster of Brazilian cembrene populations.
This study attempted to quantify the transmission of Trypanosoma cruzi in children less than 15 years of age in Barinas State, Venezuela and investigate risk factors for infection. Among 3,296 ...children, 4 (0.12%) were seropositive. The mother of one child also was also seropositive, which suggested that congenital transmission is a possible risk factor for Chagas disease in this area. Seroprevalence among the dwellers of 10 localities was 3.3%. Rhodnius prolixus was detected in 7 localities and in 8% of 125 dwellings. A multivariate logistic regression model showed that infection was associated with age, a dirt floor, and distance from houses to palm trees. The risk of infection is increased by the presence of adventitious sylvatic R. prolixus and transient or residual colonies. Insecticide spraying does not seem justified in this scenario, a finding that was also observed in other Latin American countries. New methods are therefore needed for Chagas disease control programs.
Mixed infestation of nymphs and adults of Rhodnius prolixus Stal, 1859 and Panstrongylus geniculatus Latreille, 1811 was detected in 3 (15%) of 20 dwellings in El Guamito, an endemic focus of Chagas ...disease in Lara State, Venezuela. In one of the houses, both species were positive for Trypanosoma cruzi: 14.3% (R. prolixus) and 20% (P. geniculatus ). The overall infection rate in 143 of 352 R. prolixus was 16.1%. Parasites isolated from R. prolixus were identified as T. cruzi I by random amplified polymorphic DNA analysis. Dot-enzyme-linked immunosorbent assays of 36 R. prolixus showed that 58.3% of the R. prolixus had fed on humans. The gut contents of one fifth-instar nymph of P. geniculatus that was positive for T. cruzi also reacted with anti-human serum. A questionnaire was used to gather data on the demographic and socioeconomic characteristics of the population. An indirect immunofluorescent test, an indirect hemaglutination test, and an ELISA were used to detect the presence of antibodies against T. cruzi in 84 of 86 inhabitants and in 15.5% of people more than 20 years old. The relative risk (RR) of infection was greater in men than in women (RR = 1.61, 95% confidence interval = 0.54-4.80). Of the people more than 15 years old, 36.6% had no formal education. All respondents recognized triatomine bugs, but they did not relate them to Chagas disease transmission. A total of 85.7% of the houses were "ranchos" suitable for the colonization of triatomine bugs. The possible domiciliation of P. geniculatus and the implications of competition with R. prolixus for resources are discussed. Since there is no clear separation of food sources, abiotic factors such as microclimatic variation within houses may be critical to predict the outcome of the process of competition and potential domestication of this generally sylvatic species.
We developed a mathematical model of cutaneous leishmaniasis (CL) transmission predicting CL incidence based on field data of number of positive sand flies, new CL cases, and number of susceptible ...people. We estimated the following parameters: a CL incubation period of one month, the overall susceptibility (Phi = 0.793), the serologic force of infection (lambda(m) = 0.108 /person/year, SD = 0.014), the clinical force of infection (lambda(l)= 0.114/year), the proportion of infections that result in skin lesions (alpha = 1.056), and the instantaneous reversal rate of Montenegro skin test-positive (MST(+)) people to MST(-) (rho= 0.124/year, SD = 0.021). We also provide the first field estimate of the transmission efficiency (epsilon = 0.0045, SD = 0.0009). The model predictions conform well with the observed new cases except for some small departures in the peaks and in some depressions (D(max) = 0.1494, P < 0.2). We discuss possible sources of error of our estimate of epsilon, and compare our parameter estimates with those obtained in Peru.
Predictions that deforestation would reduce American cutaneous
leishmaniasis incidence have proved incorrect. Presentations at a
recent international workshop, instead, demonstrated frequent
...domestication of transmission throughout Latin America. While posing
new threats, this process also increases the effectiveness of vector
control in and around houses. New approaches for sand fly control and
effective targeting of resources are reviewed.
Summary
A prospective study was conducted in El Brazilar, Curarigua, Lara State, Venezuela, a small rural focus of visceral leishmaniasis (VL) to investigate the burden and the evolution of ...Leishmania infection in the human and canine population. The incidence of the disease from February 1998 to February 2002 was recorded and two cross‐sectional surveys using the leishmanin skin test (LST) and immunofluorescent antibody test (IFAT) were carried out. The dipstick test with recombinant r‐K39 antigen was also applied in 2002. The incidence of the disease per year among the population (n = 118) during the period of study was 0.004. The rate of new infections per year was 0.07 95% confidence interval (95% CI): 0.15–1.09. The overall prevalence of infection measured by LST was not significantly higher in 2002 (43.2%) than in 1998 (28.3%), but it was with IFAT 16.3%vs. 4.6%; odds ratio (OR): 4.01; 95% CI: 1.03–22.78; P = 0.022 which would indicate an increasing transmission. The dipstick test only detected infection in children up to 10 years (19.4%). Prevalence in dogs was not significantly different in 2002 (57%) vs. 1998 (33%). The parasite was isolated from dogs and identified by a polymerase chain reaction based on telomeric sequences as Leishmania chagasi/infantum.
The sand fly, Lutzomyia longipalpis (Lutz & Neiva) reputedly is a complex of cryptic species; however, there is currently no consensus as to the number of species in the complex or their geographic ...distributions. We conducted phylogenetic analyses of 31 populations from throughout the species range, using seven isozyme loci and genes in the mitochondrial genome. Analyses of these two independent sets of markers were largely concordant and revealed four distinct clades that support the existence of four species. The four clades have distinct geographic ranges: (1) Brazil (Species A = Lu. longipalpis sensu stricto), (2) Laran (Species B = Lu. pseudolongipalpis), (3) cis-Andean (Species C), and (4) trans-Andean (Species D). The cis-Andean clade may be subdivided further into two groups, one in Colombia and one in northwestern Venezuela, but their taxonomic status remains unresolved. Knowledge that Lu. longipalpis is a complex of species may ultimately shed light on anomalies in the epidemiology of visceral leishmaniasis in the New World.
Antennal sensilla patterns were used to analyze population variation of domestic Rhodnius prolixus from six departments and states representing three biogeographical regions of Colombia and ...Venezuela. Discriminant analysis of the patterns of mechanoreceptors and of three types of chemoreceptors on the pedicel and flagellar segments showed clear differentiation between R. prolixus populations east and west of the Andean Cordillera. The distribution of thick and thin-walled trichoids on the second flagellar segment also showed correlation with latitude, but this was not seen in the patterns of other sensilla. The results of the sensilla patterns appear to be reflecting biogeographic features or population isolation rather than characters associated with different habitats and lend support to the idea that domestic R. prolixus originated in the eastern region of the Andes.
An indoor vector control trial was carried out between December 1996 and February 1997, with the aimof reducing the population densities of Lutzomyia ovallesi, the proven vector of cutaneous ...leishmaniasis (CL) in El Ingenio, Miranda State, Venezuela. Houses were matched according to their structure (‘bahareque’ mud and straw, concrete, and wood) and randomly assigned to a control group (n = 19) or a treated group (n = 20) that was sprayed with 25 mg/m2 of lambdacyhalothrin. This dose was selected on the basis of a laboratory susceptibility test of Lu. ovallesi to pyrethroids. Sandfly abundance was measured using CDC light traps 7–79 d post-intervention, by which time the sandfly population in control houses had declined to very low levels, at what was the end of the transmission season. Catches of total females, fed females, and males were significantly lower in sprayed than in control houses immediately after treatment. Catches of total females and males in sprayed houses recovered, reaching the level of control houses after 7 and 11 weeks, respectively. Bioassays following WHO protocols using contact cones on a sandfly laboratory colony showed a short residual effect of the insecticide explaining these results. In contrast, there was no tendency for catches of fed females in the sprayed houses to recover during the course of the trial. Previous studies of adult population dynamics showed a short season of high abundance. Combined with these results, we believe that 2 indoor sprayings with lambdacyhalothrin, the first at the beginning of November and the second at the beginning of January, would considerably reduce the Lu. ovallesi population, and control CL transmission in this and other foci where this sandfly is considered to be the main vector.
Chagas disease is a "neglected disease" affecting millions of people in Latin America. A review is made of the past successes and current challenges of the Chagas disease Control Program in Venezuela ...(PCECh), and results of recent research are presented. Officially implemented in the decade of 1960 with the aim of interrupting the intra-domestic transmission maintained by Rhodnius prolixus, the PCECh was mainly based on the large-scale use of insecticide spraying, the construction or improving of rural houses and the introduction of routine screening in public hospital blood banks for Trypanosoma cruzi using the ELISA test. After four decades, a drastic reduction of the prevalence of infection from 44.5% to 8.9% has been achieved. However, the pressure of house re-infestation by sylvan R. prolixus, and trends of domestication of other sylvan species, such as Panstrongylus geniculatus, have given rise to new epidemiological scenarias that pose new challenges. Because of this situation, re-examining how best to target monitoring and control efforts on scientific bases is of great urgency. Additionally, efforts to improve health education and community participation for a more efficient epidemiological surveillance as well as medical attention to Chagas patients, not undertaken in the past, are currently considered is a new and urgent priority of a comprehensive Chagas disease Control Program policy in Venezuela.
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